1. Field of the Invention
The present invention relates to a polishing head of a chemical mechanical polishing apparatus used for manufacturing semiconductor devices and a chemical mechanical polishing apparatus including the same. More particularly, the present invention relates to a polishing head capable of adjusting a height of a retainer ring after measuring a step height difference between the retainer ring and a semiconductor wafer.
2. Description of the Related Art
The manufacturing process of semiconductor devices demands a degree of integration, a fine pitch and a multi-layered structure of wires. As the demand increases, the surface roughness of a semiconductor wafer becomes increasingly uneven. Therefore, significant attention is paid to a technology for smoothing or planarizing a surface of the semiconductor wafer.
Known planarizing techniques include reflowing, spin on glass (SOG), etch back, and chemical mechanical polishing (CMP). Among these techniques, CMP is widely used in semiconductor device manufacturing due to an advantage of global planarization achievement, particularly in the manufacture of a semiconductor device having four wiring layers.
To perform CMP, a polishing head moves down to the semiconductor wafer, and holds the semiconductor wafer in a retainer ring thereof. Then, the polishing head presses a surface of the semiconductor wafer against a pad covering a polishing table, which is rotating. A polishing slurry is applied onto the pad during the polishing.
In addition, not only does the semiconductor wafer contact the polishing pad, but the retainer ring holding the semiconductor wafer contacts the polishing pad during the polishing, thus causing wear on the retainer ring. As the retainer ring becomes worn, a step height difference between a bottom surface of the retainer ring and the surface of the semiconductor wafer is reduced. As a result, polishing uniformity is degraded.
Several conventional apparatus have been proposed to improve polishing uniformity.
One conventional apparatus includes a polishing head having a pushing force distribution plate on a bottom thereof, the pushing force distribution plate including a plurality of segments in which a thickness of the segments is adjusted by a controller, for improving polishing uniformity by adjusting the pushing force of the semiconductor wafer.
Another conventional apparatus provides a polishing system including a modulation unit that includes a plurality of capacitors each of which includes a flexible lower plate and a plurality of smaller upper plate segments. In the polishing system, a controller monitors and adjusts the capacitance between each of the upper plate segments and the flexible lower plate, so that dynamic and localized control of polishing is achieved.
FIG. 1 illustrates a schematic view of a conventional chemical mechanical polishing (CMP) apparatus. The conventional CMP apparatus includes a polishing table 10 covered with a pad 12 that directly contacts a wafer and is rotated during polishing, a polishing head 14, that is installed over the polishing table 10 and holds a wafer 2 by vacuum suction, and a slurry supplying nozzle 18 installed over the polishing table 10 for supplying slurry from a slurry tank 16 onto the polishing table 10. The polishing head 14 is shown in greater detail in FIG. 2.
Referring to FIG. 2, the polishing head 14 includes an upper plate 20 where a vacuum tube 21 passes through at a portion thereof, and an outer ring 22 being attached to the upper plate 20 by a bolt 22a at an edge portion thereof. Inside the outer ring 22, an inner ring 24 is fixed to an inner sidewall of the outer ring 22 by pins 24a. Inside the inner ring 24, an inner plate 26 having a penetrating hole 28 connected to one end of the vacuum tube 21 is provided by being fixed to the inner ring 24 using pins 26a. 
As shown in FIG. 2 and an enlarged portion of FIG. 2, a lower plate 30 is provided under the inner plate 26 being apart from the inner plate 26 a predetermined distance and fixed to the inner plate 26 by bolts 30a. The lower plate 30 has a recess around an edge portion thereof and a plurality of vacuum holes 32 at an inner part of the recess. A porous film 34 having a plurality of holes 36 corresponding in location to the vacuum holes 32 of the lower plate 30 is provided under the lower plate 30. The wafer 2 is attached to the porous film 34 by a vacuum pumping force transferred though the vacuum holes 32 of the lower plate 30 and holes 36 of the porous film 34 from the vacuum tube 21.
Referring to the enlarged portion of FIG. 2, a retainer ring 38 is provided at the recess formed on the bottom of the lower plate 30 and clamped by a clamp ring 44 installed on an exterior of the retainer ring 38 wherein an inner tube 42 is interposed between the clamp ring 44 and the retainer ring 38. The clamp ring 44 is fixed to the lower plate 30 by bolts 44a. The retainer ring 38 is provided to prevent the wafer 2 from being pulled off outside the lower plate 30. Additionally, a shim 40 is interposed between the lower plate 30 and the retainer ring 38 at the recess to adjust a step height between a bottom of the wafer 2 and a bottom of the retainer ring 38.
The polishing head 14 contacts a back surface of the wafer 2 and tightly holds the wafer 2 using vacuum suction. The wafer 2 is fixed to the porous film 34 attached to the bottom of the polishing head 14 by a vacuum pumping force that is transferred through the vacuum tube 21, the penetrating holes 28 of the inner plate 26, the vacuum holes 32 of the lower plate 30 and holes 36 of the porous film 34.
The polishing head holding the wafer 2 by the bottom thereof using the vacuum pumping force contacts the pad 12 of the polishing table 10, which is rotating and presses the wafer against the pad 12, thereby polishing the surface of the wafer.
At this time, a slurry is supplied onto the polishing table 10 from the slurry tank 16 via the slurry nozzle 18, so that mechanical and chemical polishing is accomplished.
The wafer 2 may not be detached from the polishing head 14, even though the vacuum pumping force is removed from the vacuum tube 21, due to a pressing force of the polishing head 14 and a clamping force of the retainer ring 38 during polishing.
The retainer ring 38, however, is gradually worn-out as the polishing proceeds due to the nonuniform distribution of the pressing force. Further, the retainer ring 38 may be worn-out due to the internal pressure variation of the internal tube 42 pressing the retainer ring 38. As a result, polishing uniformity of the wafer is degraded.
In a case when the retainer ring 38 becomes worn-out, an operator releases the retainer ring 38 from the polishing head 14 and replaces the shim 40 installed between the lower plate 30 and the retainer ring 38, thereby increasing a step height difference between the wafer 2 and the retainer ring 38. However, it is difficult to detect the worn-out status of the retainer ring in real time. Accordingly, inferior polishing frequently occurs.
Further, such replacements are labor-intensive work and an accuracy of adjustment of the step height difference between the wafer and the retainer ring is low because the replacement is performed manually.
It is a feature of an embodiment of the present invention to provide a polishing head capable of automatically detecting a step height difference between a wafer and a retainer ring and accurately adjusting the step height difference, and a chemical mechanical polishing apparatus including the same polishing head.
In accordance with one aspect of the present invention, there is provided a polishing head for a chemical mechanical polishing apparatus including a plate having a plurality of vacuum holes for transferring a vacuum pumping force; a porous film having a plurality of holes corresponding to the locations of the plurality of vacuum holes, the porous film being attached to a lower surface of the plate; a retainer ring attached to the lower surface of the plate at edge portion thereof and having a sloped surface; a clamp ring attached to the lower surface of the plate adjacent the retainer ring for clamping the retainer ring; an adjusting ring having a sloped surface parallel and in contact with the sloped surface of the retainer ring, the adjusting ring being installed between the retainer ring and the plate; and a diameter adjusting device for adjusting a diameter of the adjusting ring by moving the adjusting ring along the sloped surface of the retainer ring, thereby adjusting a height of the retainer ring.
Preferably, the adjusting ring includes a first half ring having tabs at both ends thereof and a second half ring having notches for receiving the tabs of the first half ring at both ends thereof, wherein the tabs and the notches form an adjustably mating connection to vary the diameter of the adjusting ring.
Preferably, the diameter adjusting device includes a first connection bar and a second connection bar extending upwardly from an upper surface of the first half ring and an upper surface of the second half ring, respectively; a third connection bar and a fourth connection bar connected to the first connection bar and the second connection bar, respectively, the third and fourth connection bars being perpendicular to the first and second connection bars, wherein the third connection bar and the fourth connection bar are arranged longitudinally, and the third connection bar and the fourth connection bar have screw threads on outer surfaces thereof, and wherein a direction of the screw threads of the third connection bar is opposite to a direction of the screw threads of the fourth connection bar; an adjusting bar having a central hole, the central hole of the adjusting bar having screw grooves corresponding to the screw threads of the third connection bar and the fourth connection bar on an inner wall thereof; and a groove formed in a lower portion of the plate for receiving the adjusting bar, the first and second connection bars, and the third and the fourth connection bars.
Preferably, the adjusting bar has gear grooves on an outer surface thereof for receiving a gear therein. Also preferably, the polishing head includes a gear for rotating the adjusting bar, the gear being connected to a rotating shaft that is rotated by an external actuating unit.
In accordance with another aspect of the present invention, there is provided a chemical mechanical polishing apparatus for manufacturing a semiconductor device including a polishing table capable of rotating at a predetermined speed, the polishing table being covered with a pad; a slurry supplying nozzle for supplying a slurry onto the pad of the polishing table; a polishing head, capable of rotating, for holding a wafer and pressing the wafer to the pad of polishing table while rotating, the polishing head having a retainer ring for securing the wafer; and a step height difference measuring device for measuring a height difference between the wafer and the retainer ring.
In accordance with yet another aspect of the present invention, there is provided a chemical mechanical polishing apparatus for manufacturing a semiconductor device, including a polishing table covered with a pad, the polishing table being capable of rotating at a predetermined speed; a slurry supplying nozzle for supplying slurry onto the pad of the polishing table; and a polishing head, including a plate having a plurality of vacuum holes for transferring a vacuum pumping force; a porous film having a plurality of holes corresponding to the locations of the plurality of vacuum holes, the porous film being attached to a lower surface of the plate; a retainer ring attached to the lower surface of the plate at an edge portion thereof and having a sloped surface; a clamp ring attached to the lower surface of the plate adjacent the retainer ring for clamping the retainer ring; an adjusting ring having a sloped surface parallel and in contact with the sloped surface of the retainer ring, the adjusting ring being installed between the retainer ring and the plate; and a diameter adjusting device for adjusting a diameter of the adjusting ring by moving the adjusting ring along the sloped surface of the retainer ring, thereby adjusting a height of the retainer ring.
Preferably, the step height difference measuring device measures the step height difference using a micro gauge that measures electrical signals which are generated in response to a movement variation width of an elastic probe that moves along a surface of the retainer ring and a surface of the wafer.